Reportable Business Segments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues		$ 1,320	$ 1,817
Operating Income		166	160
Assets		8,654		$ 9,141
Equity in earnings of unconsolidated affiliate, net		60	52
Investment in unconsolidated affiliate		2,580		2,594
Natural Gas Distribution
Segment Reporting Information [Line Items]
Revenues		888	1,185
Operating Income		160	146
Energy Services
Segment Reporting Information [Line Items]
Revenues		432	632
Operating Income		6	13
Midstream Investments (1)
Segment Reporting Information [Line Items]
Revenues	[1]	0	0
Operating Income	[1]	0	0
Other Operations
Segment Reporting Information [Line Items]
Revenues		0	0
Operating Income		0	1
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues		(14)	(26)
Assets		(829)		(744)
Intersegment Eliminations | Natural Gas Distribution
Segment Reporting Information [Line Items]
Revenues		(7)	(8)
Intersegment Eliminations | Energy Services
Segment Reporting Information [Line Items]
Revenues		(7)	(18)
Intersegment Eliminations | Midstream Investments (1)
Segment Reporting Information [Line Items]
Revenues	[1]	0	0
Intersegment Eliminations | Other Operations
Segment Reporting Information [Line Items]
Revenues		0	0
Operating Segments [Member] | Natural Gas Distribution
Segment Reporting Information [Line Items]
Assets		5,661		5,657
Operating Segments [Member] | Energy Services
Segment Reporting Information [Line Items]
Assets		844		857
Operating Segments [Member] | Midstream Investments (1)
Segment Reporting Information [Line Items]
Assets	[1]	2,580		2,594
Operating Segments [Member] | Other Operations
Segment Reporting Information [Line Items]
Assets		398		777
Enable Midstream Partners [Member]
Segment Reporting Information [Line Items]
Investment in unconsolidated affiliate		2,580		2,594
Enable Midstream Partners [Member] | Midstream Investments (1)
Segment Reporting Information [Line Items]
Equity in earnings of unconsolidated affiliate, net		60	$ 52
Investment in unconsolidated affiliate		$ 2,580		$ 2,594

[1] Midstream Investments’ equity earnings are as follows: Three Months Ended March 31, 2016 2015 (in millions)Enable $60 $52Midstream Investments’ total assets are as follows: March 31, 2016 December 31, 2015 (in millions)Enable $2,580 $2,594